A simple worker

worker.js

function worker (key, options = {}, work) {
    global.queues = global.queues || {}
    global.queues[key] = global.queues[key] || []
    global.queues[`${key}:active`] = global.queues[`${key}:active`] || []
    global.queues[`${key}:completed`] = global.queues[`${key}:completed`] || []
    global.queues[`${key}:failed`] = global.queues[`${key}:failed`] || []

    const queue = global.queues[key]

    this.jobs = this.jobs || 0

    const MAX_JOBS = options.concurrency || 1

    const status = (job, status) => {
        const queue = (!status || status === 'pending') ? global.queues['process'] : global.queues[`process:${status}`]

        const isStatus = ((queue || []).indexOf(job) > -1)

        return isStatus
    }

    const active = (job, status) => {
        const queue = global.queues['process:active']

        if (status === true) {
            if (status(job, 'active')) {
                queue.push(job)
            }
        } else if (status === false) {
            delete queue[queue.indexOf(job)]
        }
    }

    const done = (error, job) => {
        this.jobs--

        if (!job) return

        active(job, false)

        const queue = error ? global.queues['process:failed'] : global.queues['process:successful']

        queue.push({...job, error})
    }

    setInterval(() => {
        if (this.jobs <= MAX_JOBS) {
            this.jobs++

            const job = queue.pop()

            if (job) {
                active(job, true)

                work({queue, job, active, done})

            } else {
                done()
            }
        }
    }, 1000)

    return {
        push: (job) => {
            const exist = this.isComplete(job) || this.isPending(job)

            if (!exist) {
                queue.push(job)
            }

            return exist
        },
        isPending: (job) => {
            return status(job, 'pending')
        },
        isActive: (job) => {
            return status(job, 'active')
        },
        isSuccessful: (job) => {
            return status(job, 'successful')
        },
        isFailed: (job) => {
            return status(job, 'failed')
        },
        isComplete: (job) => {
            return this.isSuccessful(job) || this.isFailed(job)
        },
    }
}